Date: Mon, 07 Jul 2014 10:12:07 +0200 From: Hans Petter Selasky <hps@selasky.org> To: freebsd-net@freebsd.org, freebsd-current@FreeBSD.org Subject: [RFC] Allow m_dup() to use JUMBO clusters Message-ID: <53BA5657.8010309@selasky.org>
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Hi,
I'm asking for some input on the attached m_dup() patch, so that
existing functionality or dependencies are not broken. The background
for the change is to allow m_dup() to defrag long mbuf chains that
doesn't fit into a specific hardware's scatter gather entries, typically
when doing TSO.
In my case the HW limit is 16 entries of length 4K for doing a 64KByte
TSO packet. Currently m_dup() is at best producing 32 entries of each 2K
for a 64Kbytes TSO packet.
By allowing m_dup() to get JUMBO clusters when allocating mbufs, we
avoid creating a new function, specific to the hardware, to defrag some
rare-occurring very long mbuf chains into a mbuf chain below 16 entries.
Any comments?
--HPS
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=== uipc_mbuf.c
==================================================================
--- uipc_mbuf.c (revision 268358)
+++ uipc_mbuf.c (local)
@@ -917,7 +917,15 @@
struct mbuf *n;
/* Get the next new mbuf */
- if (remain >= MINCLSIZE) {
+ if (remain >= MJUM16BYTES) {
+ /*
+ * By allocating a bigger mbuf, we get fewer
+ * scatter gather entries for the hardware to
+ * process:
+ */
+ n = m_getjcl(how, m->m_type, 0, MJUM16BYTES);
+ nsize = MJUM16BYTES;
+ } else if (remain >= MINCLSIZE) {
n = m_getcl(how, m->m_type, 0);
nsize = MCLBYTES;
} else {
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